1. Field of the Invention
The present invention is directed to an optical waveguide amplifier for use in telecommunication systems and more particularly, an optical waveguide amplifying fiber providing high absorption and efficiency.
2. Technical Background
The continuous growth of bandwidth requirements in optical-based communication systems has resulted in a large demand for systems able to operate within several optical wavelength ranges including the S-band optical range, the C-band optical range and the L-band optical range. The S-band is typically defined as the wavelengths between about 1465 nm and about 1525 nm, which lies below the C-band wavelength range which extends between about 1525 nm and about 1570 nm, which in turn lies just below the L-band wavelength range which extends between about 1570 nm and 1605 nm. In order to meet this explosive growth and demand for capacity in fiber optic transmission systems, system designers have begun to investigate those spectral regions lying beyond the conventional or C-band transmission band, including the aforementioned S-band and L-band wavelength ranges.
Erbium-doped fiber amplifiers are used to provide amplification in optical transmission systems, and particularly for deployment within those systems operating within the C-band wavelength range. Application of erbium doped fiber amplifiers within the telecommunication systems operating within the L-band wavelength range can be problematic in that lower excited-state population inversions are necessary to provide sufficiently flat gain spectra across the L-band wavelength range. Thus, longer lengths of fiber within the erbium doped fiber amplifier or higher erbium concentrations therein are necessary to provide the same gain which would be provided within a given erbium doped fiber amplifier operating within the C-band wavelength range.
The longer lengths of fiber required in erbium doped fiber amplifiers utilized within the L-band wavelength range results in a decrease in fiber efficiency and an increase in noise when compared with erbium doped fiber amplifiers. In addition, non-linear effects such as four-wave mixing and cross talk modulation are more severe. Typically, the effective areas of erbium doped fiber amplifiers are increased in an attempt to improve the xe2x80x9clinearityxe2x80x9d of the erbium doped fiber amplifiers. The reasoning for this approach has been that an increase in the effective area spreads out the optical power being transmitted through the doped region of the associated erbium doped fiber amplifier, thereby reducing the intensity of the optical power at any given point. This, in turn, yields an erbium doped fiber amplifier exhibiting more linear material behavior.
The spectroscopy of erbium within L-band erbium doped fiber amplifiers thus poses several challenges with respect to designing the fiber amplifier to be used therein. These challenges include: (1) packaging amplifier modules with longer fiber lengths, as required by the lower differential gain while controlling fiber bend loses at longer wavelengths, (2) maintaining a high absorption rate without significantly increasing concentration quenching, (3) minimizing non-linear effects such as two-channel four-wave mixing and cross-phase modulation in the amplifier, and (4) minimizing the intrinsically higher L-band noise figure.
This invention relates to an optical waveguide fiber amplifier that effects amplification of an optical signal within the L-band optical wavelength range. More specifically, the invention relates to a high efficiency optical waveguide amplifier operating in the L-band optical wavelength range providing reduced non-linearity effects and a reduced noise figure.
In a first embodiment, an optical waveguide fiber comprises a core region having a relative refractive index percent and an outer radius, wherein the core region, at least in part, comprises Er2O3 within the range of from about 1300 wt.ppm to about 3600 wt.ppm, Al2O3 within the range of from about 6.0 wt. % to about 10.0 wt. % and GeO2 within the range of from about 9.0 wt. % to about 20.0 wt. %. The optical waveguide fiber also comprises an inner clad surrounding the core region and having a relative refractive index percent and an outer radius, and an outer clad surrounding the inner clad and having a relative refractive index percent. The relative refractive index percentages and radii of the core region, the inner clad and the outer clad are chosen from the following ranges: the relative refractive index percent of the core segment within the range of from about 0.5% to about 2%; the relative refractive index percent of the inner clad within the range of from about 0.0% to about 0.4%; the outer radius of the core region within the range of from about 0.7 xcexcm to about 1.6 xcexcm; and, the outer radius of the inner clad within the range of from about 4.3 xcexcm to about 18.8 xcexcm.
In a second embodiment, an optical waveguide fiber comprises a core region having a refractive index profile and, at least in part, comprises Er2O3 within the range of from about 1300 wt.ppm to about 3600 wt.ppm, Al2O3 within the range of from about 6.0 wt. % to about 10.0 wt. % and GeO2 within the range of from about 9.0 wt. % to about 20.0 wt. %. The optical waveguide fiber also comprises an inner clad surrounding the core region and having a refractive index profile, and an outer clad surrounding the inner clad and having a refractive index profile. The amounts of Er2O3, Al2O3 and GeO2 within the core region and the refractive index profiles of the core region, the inner clad and the outer clad are selected to provide a mode field diameter of greater than or equal to about 5.2 xcexcm at a wavelength of about 1550 nm.
The present invention also includes optical communication systems employing the optical waveguide fibers and optical waveguide fiber amplifiers in accordance with the embodiments described above.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the following description together with the claims and appended drawings.